The invention relates to a control device for a process valve unit which has a valve drive and a valve fitting, wherein the control device has a control unit which is configured to receive a control signal from a superordinate control, preferably a memory-programmable control such as a programmable logic controller, via a communication interface which is provided in the field level, and to control the valve drive in accordance with the control signal.
Such a control device can be constructed as a positioner, position adjuster and/or control head and is used to set the position of a valve member of the valve fitting by controlling the valve drive. A process fluid flows through the valve fitting during operation. By setting the valve member, a process fluid flow can be controlled. The valve member can be moved, for example, into an open or closed position in order to release or block the process fluid flow. It may further be possible to move the valve member into one or more positions between the open and closed position in order thus to set a throughflow rate of the process fluid flow.
The control of the valve drive by the control device is brought about in accordance with a control signal which is produced by the superordinate control—for example, a memory-programmable control such as a programmable logic controller (PLC) from the control level—and which is transmitted to the field level via a communication connection. The control signal can be transmitted in a message, for example. In the field level, the control signal is received by a communication interface which can be provided, for example, at the control device. The communication interface is in particular a digital interface, such as, for example, a field bus interface, or an analogue interface, such as, for example, an analogue current interface.
The control of the valve drive in accordance with the control signal is carried out in particular on the basis of a control and/or regulator model which is adapted to the valve fitting or the valve drive and which is stored in the control unit. The control and/or regulator model can preferably be adapted to the valve fitting or the valve drive by configuration parameters.
From the prior art, it is known to provide a control device with a maintenance interface, to which a manual operation device, for example, a maintenance device, in particular a handheld device, can be directly connected in order to carry out specific maintenance processes. In this instance, the maintenance interface is typically constructed as a point-to-point interface, that is to say, the maintenance interface is only suitable for establishing a direct connection with a single connected device—the manual operation device—and for communicating therewith.